I'm sorry to have to disagree, but "wife/husband of [many] years" is an idiom implying [many] years of marriage. For example, look at the primary hits from "wife of thirty years" in Google.I would go with b, but you could make it to mean "a"
His wife of the age of thirty years, is about to leave him (Kind of akward, but one can understand)
His thirty year old wife is about to leave him (Most natural)
His wife aged thirty is about to leave him (UK)